Encyclopedia of Health and Medicine

E–I
efficacy The ability of a DRUG to produce a predictable
effect in the body. Many factors influence
a drug’s efficacy, from foods and other drugs to
health conditions and a person’s metabolic characteristics.
An individual’s age, weight, gender, and
level of activity also may affect the rate at which a
drug enters, and how long it stays in, the BLOOD
circulation. Efficacy is a key factor in determining
a drug’s potential effectiveness to treat a particular
condition in a specific individual. Some drugs
have greater efficacy in younger people, for example.
Other factors that are also relevant include
BIOAVAILABILITY and BIOEQUIVALENCE.
See also CYTOCHROME P450 (CYP450) ENZYMES;
THERAPEUTIC WINDOW.
formulary A list of the prescription drugs a
health plan or insurance company, including state
and federal health insurance programs, will cover.
Typically a committee of physicians and pharmacists
makes the determinations about what drugs
appear in the formulary and why. Factors for consideration
include
• the DRUG’s EFFICACY
• whether generic products are available
• similarity to other drugs that are less expensive
or have fewer side effects
• NARROW THERAPEUTIC INDEX (NTI) status
• the need for the drug within the insurer’s
patient population
• whether over-the-counter forms of the drug are
available
• the drug’s approved uses
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Most insurers update their formularies at least
annually. An insurer may pay a smaller percentage
of the cost for a nonformulary drug or may
choose not to cover (pay for) nonformulary drugs
at all except within the parameters of specifically
defined criteria. A doctor may prescribe a drug
that is not on the formulary even though the
insurer may refuse to pay for it. The person may
still receive the drug by paying for the prescription.
Drug formularies help establish consistent
prescribing practices as well as control costs for the
insurer.
See also GENERIC DRUG; ORANGE BOOK, THE; OVER-
THE-COUNTER (OTC) DRUGS; PHARMACOPEIA; SIDE
EFFECT.
generic drug A DRUG that has BIOEQUIVALENCE and
THERAPEUTIC EQUIVALENCE to its INNOVATOR DRUG (the
first drug to receive approval for use). Generic
drugs became significant in the health-care industry
in the 1970s when manufacturing requirements
and procedures became standardized and
patents began to expire on innovator drugs, converging
factors that opened the market for competition
within the pharmaceutical industry. Most
generic drugs are significantly less expensive than
their innovator counterparts, and most states have
laws allowing pharmacies to substitute generic
drugs when filling prescriptions unless the prescribing
provider specifies otherwise. The intent
behind such laws is to provide consumers with
cost-effective alternatives for prescription drugs.
Generic products are also available for many OVER-
THE-COUNTER (OTC) DRUGS, allowing consumers to
choose either generic or trade name products.
The US Food and Drug Administration (FDA),
the federal regulatory agency that approves drugs
for use in the United States, establishes the criteria
for potency, purity, consistency, and efficacy all
drugs must meet. These criteria are the same for